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/*------------------------------------------------------------------------- * * slru.h * Simple LRU buffering for transaction status logfiles * * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * src/include/access/slru.h * *------------------------------------------------------------------------- */ #ifndef SLRU_H #define SLRU_H #include "access/xlogdefs.h" #include "storage/lwlock.h" /* * Define SLRU segment size. A page is the same BLCKSZ as is used everywhere * else in Postgres. The segment size can be chosen somewhat arbitrarily; * we make it 32 pages by default, or 256Kb, i.e. 1M transactions for CLOG * or 64K transactions for SUBTRANS. * * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF, * page numbering also wraps around at 0xFFFFFFFF/xxxx_XACTS_PER_PAGE (where * xxxx is CLOG or SUBTRANS, respectively), and segment numbering at * 0xFFFFFFFF/xxxx_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need * take no explicit notice of that fact in slru.c, except when comparing * segment and page numbers in SimpleLruTruncate (see PagePrecedes()). * * Note: slru.c currently assumes that segment file names will be four hex * digits. This sets a lower bound on the segment size (64K transactions * for 32-bit TransactionIds). */ #define SLRU_PAGES_PER_SEGMENT 32 /* * Page status codes. Note that these do not include the "dirty" bit. * page_dirty can be TRUE only in the VALID or WRITE_IN_PROGRESS states; * in the latter case it implies that the page has been re-dirtied since * the write started. */ typedef enum { SLRU_PAGE_EMPTY, /* buffer is not in use */ SLRU_PAGE_READ_IN_PROGRESS, /* page is being read in */ SLRU_PAGE_VALID, /* page is valid and not being written */ SLRU_PAGE_WRITE_IN_PROGRESS /* page is being written out */ } SlruPageStatus; /* * Shared-memory state */ typedef struct SlruSharedData { LWLockId ControlLock; /* Number of buffers managed by this SLRU structure */ int num_slots; /* * Arrays holding info for each buffer slot. Page number is undefined * when status is EMPTY, as is page_lru_count. */ char **page_buffer; SlruPageStatus *page_status; bool *page_dirty; int *page_number; int *page_lru_count; LWLockId *buffer_locks; /* * Optional array of WAL flush LSNs associated with entries in the SLRU * pages. If not zero/NULL, we must flush WAL before writing pages (true * for pg_clog, false for multixact, pg_subtrans, pg_notify). group_lsn[] * has lsn_groups_per_page entries per buffer slot, each containing the * highest LSN known for a contiguous group of SLRU entries on that slot's * page. */ XLogRecPtr *group_lsn; int lsn_groups_per_page; /*---------- * We mark a page "most recently used" by setting * page_lru_count[slotno] = ++cur_lru_count; * The oldest page is therefore the one with the highest value of * cur_lru_count - page_lru_count[slotno] * The counts will eventually wrap around, but this calculation still * works as long as no page's age exceeds INT_MAX counts. *---------- */ int cur_lru_count; /* * latest_page_number is the page number of the current end of the log; * this is not critical data, since we use it only to avoid swapping out * the latest page. */ int latest_page_number; } SlruSharedData; typedef SlruSharedData *SlruShared; /* * SlruCtlData is an unshared structure that points to the active information * in shared memory. */ typedef struct SlruCtlData { SlruShared shared; /* * This flag tells whether to fsync writes (true for pg_clog and multixact * stuff, false for pg_subtrans and pg_notify). */ bool do_fsync; /* * Decide which of two page numbers is "older" for truncation purposes. We * need to use comparison of TransactionIds here in order to do the right * thing with wraparound XID arithmetic. */ bool (*PagePrecedes) (int, int); /* * Dir is set during SimpleLruInit and does not change thereafter. Since * it's always the same, it doesn't need to be in shared memory. */ char Dir[64]; } SlruCtlData; typedef SlruCtlData *SlruCtl; extern Size SimpleLruShmemSize(int nslots, int nlsns); extern void SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, LWLockId ctllock, const char *subdir); extern int SimpleLruZeroPage(SlruCtl ctl, int pageno); extern int SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok, TransactionId xid); extern int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid); extern void SimpleLruWritePage(SlruCtl ctl, int slotno); extern void SimpleLruFlush(SlruCtl ctl, bool checkpoint); extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage); typedef bool (*SlruScanCallback) (SlruCtl ctl, char *filename, int segpage, void *data); extern bool SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data); /* SlruScanDirectory public callbacks */ extern bool SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data); extern bool SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int segpage, void *data); #endif /* SLRU_H */